Hi, I was trying to build a graph from an edge list and ran into some problems. The following code throws an exception on write_graphviz(). I think it is because there's no property map called node_id in the graph. import boost.graph as bgl edges = [ ( 'a', 'b' ), ( 'b', 'c' ), ( 'c', 'a' ) ] g = bgl.Graph( edges ) g.write_graphviz( 'bind-copy.dot' ) I get the following: Traceback (most recent call last): File "<stdin>", line 1, in ? KeyError: 'node_id' I couldn't manage to generate the node_id property map automatically. So after you have built the graph with the edge list constructor how do you know which vertex is which? I ended up using the following code to create the graph: def build( edges ): # Create a graph to build g = bgl.Graph() # Construct some property maps node_ids = g.vertex_properties[ 'node_id' ] = g.vertex_property_map( 'string' ) color = g.vertex_properties[ 'color' ] = g.vertex_property_map( 'string' ) centrality = g.vertex_properties[ 'centrality' ] = g.vertex_property_map( 'float' ) weight = g.edge_properties[ 'weight' ] = g.edge_property_map( 'float' ) length = g.edge_properties[ 'len' ] = g.edge_property_map( 'float' ) # create the edges and vertices name_2_vertex = { } for ( name1, name2 ) in edges: if not name_2_vertex.has_key( name1 ): v1 = name_2_vertex[ name1 ] = g.add_vertex() node_ids[ v1 ] = name1 else: v1 = name_2_vertex[ name1 ] if not name_2_vertex.has_key( name2 ): v2 = name_2_vertex[ name2 ] = g.add_vertex() node_ids[ v2 ] = name2 else: v2 = name_2_vertex[ name2 ] e = g.add_edge( v1, v2 ) weight[ e ] = 0.1 length[ e ] = 4 # Color articulation points red for v in bgl.biconnected_components( g ): color[ v ] = 'red' # Assign centrality values to property map bgl.brandes_betweenness_centrality( g, centrality ) return g This code seems to works fine. So I thought I'd post this just to see if I was missing something obvious and/or in the hope someone else might find it useful. Best, John.